The identification of individual electrical circuits, as they connect to outlets and light fixtures, in existing buildings is often the subject of much time consuming effort. In particular, when a building is being renovated, say for subdivision into apartments, it is important to know that the power for one apartment unit is not mistakenly hooked into another apartment unit. It is usually impractical to visually check wire routing or connections, because the wiring is hidden behind walls, etc. Therefore, much time is wasted by electricians or other tradesmen in merely verifying that outlets and fixture connections are unique to each apartment and do not cheat the future tenant by a mix-up in wiring which avails his power to another apartment unit.
Equally important is the verification of load distribution for electrical wiring circuits in new as well as older buildings, such as homes. Clearly it is poor, if not illegal, practice to have an excessive number of outlets or fixtures on one circuit, while loading of another circuit may be minimal. Building codes in many areas require that a limited number of outlets are allowed on most circuits, and that independent circuits must be provided in high use areas, such as kitchens, etc. It is oftimes a requirement now that ground-fault interrupters protect certain circuit branches, and these present a special case for verification by an inspector. Once construction has advanced beyond a certain point (e.g., walls are closed in), or more especially in older buildings that are under renovation, it is, for all practical purposes, impossible to visually acertain circuit distribution by mere inspection of wire routing. It is under these conditions that the tradesman, or the electrical inspector, must rely upon other techniques to verify proper wiring load distribution. Brute force methods are most often relied upon, whereupon power is interrupted from (or applied to) but one of several circuits, and the tradesman runs about checking for presence or absence of power at each and every outlet and fixture in the building. Obviously error is the rule of the day using such a technique, due to the characteristic of human nature for taking short-cuts, or overlooking obscure outlets or fixtures. In large buildings, say an apartment building containing many units, or a commercial building, the importance for verifying circuit distribution is at least just as important as in a small building, such as a modest home, but the physical task of verification is of much greater magnitude and, in some cases, economically impractical. Given a building, such as an old house that is undergoing subdivision and renovation into condiminium or apartment units, there might be 100 or more outlets, light fixtures, and other terminations for the electrical wiring. If an electrician finds there are, for example, 12 separate wiring circuits which need to be verified, the mere allotment of 30 seconds to verify each outlet or fixture would consume 50 minutes per circuit, or conceivably 50 minutes multiplied by the 12 separate circuits, for a total of 10 hours to 100% verify the circuit connections. Simple economics dictate that 100% verification is impractical, even for this modest example. Therefore mix-ups in the circuits between housing units, where one tenant pays for another tenant's use is common. More importantly, safety factors are compromised, because true total circuit loading (e.g., how many outlets does a circuit really serve) is unknown and dangerous electrical overload may occur.
The role of a town electrical inspector is to, among other things, verify compliance with electrical codes and rules pertaining to wiring power distribution and the like in new as well as older buildings. There is an implicit responsibility thurst upon the inspector that he certify that the wiring distribution is proper and safe and, as such, there is a need for the electrical inspector to conduct an efficient and thorough checkout of the wiring network in any building which is subject for an inspector's approval. Unfortunately, the time constraints under which civil inspectors oftimes operate may contribute to their shunning all-inclusive inspection, or even an extensive amount of spot checking, of wiring load distribution. The result is less-than-complete inspection which can lead to unsafe building power distribution which can, at best, cause light-dimming and blown fuses due to overload, or else more sadly to damage or loss of a building or even human life due to fire caused by improper circuit power distribution. Additionally, the economic distress caused by cross-over of wire routing between one apartment or condimimum unit and another may be of considerable import to tenants of a multi-dwelling building.
The installation or troubleshooting of telephone circuits, and even other "low-voltage" circuits such as thermostat lines, doorbell circuits, annunciators, and the like in buildings is also subject for utilization of the advantages now taught by my instant invention. For example, a telephone installer can excite several telephone lines with the tag signals and then merely read out which line he connects to at the other end of any wires and cables which are buried in building walls. In a like way, thermostat wire runs and the like can be sorted out and verified as to "where they go", thereby saving much time for the tradesman and averting improper operation of whatever apparatus the tested circuit connects between.
Earlier teachings show much in the way of devices that light bulbs or produce sounds when "ringing out" circuits. However, these earlier artisans did not bring forth a device such as is now taught which allows simple unambiguous indication of exactly which circuit is being connected with at any of an essentially unlimited number of locations throughout a building. In particular, the inventor's of these earlier devices were silent regarding the use, as I now introduce, of a high frequency carrier signal which is uniquely modulated with a pulse train that can be detected and converted into an unambiguous indication for even a layperson.